Long-Term Changes in the Size of Pituitary Microadenomas

Background: The estimated prevalence of pituitary lesions is 10% to 38.5% in radiologic studies. However, how frequently these incidental lesions should be monitored by serial pituitary magnetic resonance imaging (MRI) remains unclear.Objective: To evaluate changes in pituitary microadenomas over time.Design: Retrospective, longitudinal cohort study.Setting: Mass General Brigham, Boston, Massachusetts.Patients: Evidence of pituitary microadenoma from MRI.Measurements: Dimensions of pituitary microadenomas.Results: During the study period (from 2003 to 2021), 414 patients with pituitary microadenomas were identified. Of the 177 patients who had more than 1 MRI, 78 had no change in the size of the microadenoma over time, 49 had an increase in size, 34 had a decrease in size, and 16 had both an increase and decrease in size. By linear mixed model analysis, the estimated slope was 0.016 mm/y (95% CI,-0.037 to 0.069). In the subgroup analysis, pituitary adenomas with a baseline size of 4 mm or less tended to increase in size. The estimated slope was 0.09 mm/y (CI, 0.020 to 0.161). In contrast, in the subgroup with baseline tumor size greater than 4 mm, the size tended to decrease. The estimated slope was-0.063 mm/y (CI,-0.141 to 0.015).Limitation: Retrospective cohort, some patients were lost to follow-up for unknown reasons, and data were limited to local large institutions.Conclusion: During the study period, approximately two thirds of the microadenomas remained unchanged or decreased in size. The growth, if any, was slow. These findings suggest that less frequent pituitary MRI surveillance for patients with incidental pituitary microadenomas may be safe.